#include <iostream>
#include <algorithm>
#include <cstring>

using namespace std;

#define int long long
const int N = 1e5 + 10;
int a[N];
int len , n , k;
bool check(int x)
{
    int cnt = 0;
    for(int i = 2;i <= n;i ++)
    {
        int d = a[i] - a[i - 1];
        cnt += d / x;
        if(d % x == 0) cnt--;
    }
    return cnt <= k;
}
signed main()
{
    cin >> len >> n >> k;
    for(int i = 1;i <= n;i ++) cin >> a[i];
    int l = 1 , r = len;
    while(l < r)
    {
        int mid = l + r >> 1;
        if(check(mid)) r = mid;
        else l = mid + 1;
    }
    cout << r << endl;
    return 0;
}